Profiat Duran, Hebrew name Isaac Ben Moses Ha-levi, pseudonym Efod or Efodi (born c. 1350, Perpignan?, France—died c. 1415) Jewish philosopher and linguist, the author of a devastating satire on medievalChristianity and of a notable work on Hebrew grammar.

Duran was the descendant of a scholarly Jewish family of southern France. He was educated in Germany and then took a position as tutor with a wealthy family in Catalonia. There, in 1391, in a wave of Spanish religious persecution, he was compelled to profess Roman Catholicism. Like many other ostensibly converted Spanish Jews, he continued his own religious observances in secret, and, after leaving Spain, he openly resumed the practice of Judaism.

Earlier, however, he had planned to travel to Palestine with another forcibly converted Spanish Jew, but the journey was abandoned when Duran received a letter from his fellow convert indicating his desire to remain a Roman Catholic and urging Duran also to remain true to Christianity. Duran’s response, the celebrated letter ʿAl tehi ka-ʾavotekha (“Be Not like Thy Fathers”), portrayed with subtle irony what he saw as the irrationality of Christian doctrine and summarized with feigned naiveté the worst abuses of the contemporary church. So artful was the satire that the epistle, widely circulated in Spain, was initially greeted by Christians as a defense of their religion. Once its true nature was understood, copies of the work were publicly burned. (It was later published at Constantinople in 1554).

In conjunction with the letter, Duran also wrote an anti-Christian polemic, Kelimat ha-Goyim (“Shame of the Gentiles”), in about 1397, which discredited the Gospels and other early Christian writings.

Duran’s lasting reputation is based not so much on his polemical writings as on his Hebrew grammar, Maʾaseh Efod (1403), a work of the highest scholarship. His other written works include a history of Jewish martyrs.